The invention relates to a method of operating an internal combustion engine which has a cooling circuit.
Modern internal combustion engines achieve high levels of thermodynamic efficiency. This results in new conflicts of objectives with regard to the heat budget of the engines. On the one hand, a rapid heat-up phase after the cold start is desirable, in order to reduce the friction by heating of the oil and to achieve optimum combustion as quickly as possible. However, implementing measures aimed at achieving high engine efficiency, delays the heating of the interior of the vehicle, since the coolant which flows through a heater is not heated sufficiently quickly, to achieve a satisfactory heating comfort. It is therefore necessary to provide secondary heating means.
German laid-open specification DE 197 28 351 A1 discloses a method for regulating heat in an internal combustion engine in which component temperatures and output characteristic variables of the internal combustion engine are monitored and are taken into account in the control of the coolant flow. Speed-controlled pumps, fans, electrically actuable valves and shutters can be used to implement the control.
It is the object of the present invention to provide a method of operating an internal combustion engine, and a motor vehicle, with which a satisfactory heating comfort is achieved without the need for secondary heating means.
In a method for operating an internal combustion engine, and a motor vehicle to be heated by the engine coolant, wherein the internal combustion engine has a cooling circuit, a heating mode can be established in which operating parameters of the internal combustion engine, while satisfying required output set values, are set for the maximum possible introduction of heat into the coolant and the exhaust gas in order to reach or hold a desired coolant temperature.
The coolant can be heated rapidly if, during the startup phase, the internal combustion engine is briefly switched to an operation with a thermodynamic efficiency, which is as bad as possible while still ensuring proper operation while the required output set values are satisfied. Consumption and exhaust-gas limit values can be maintained by switching to the heating mode only for a short period. Switching to the heating mode makes it possible to avoid the need for secondary heating means.
In a particular embodiment of the invention, in order to increase a combustion-chamber surface temperature during the startup phase, combustion is temporarily advanced with respect to the standard operation, while a maximum possible combustion-chamber pressure is maintained.
Advancing the combustion and/or maintaining the flow of coolant allows the combustion-chamber surface to be heated as quickly as possible. This is a required condition for operation with the worst possible thermodynamic efficiency, since misfiring can only be avoided with a high combustion-chamber surface temperature. Therefore, if the combustion-chamber surface temperature sensed is below a predetermined threshold value, above which the engine can be operated with a poor thermodynamic efficiency, the combustion timing is initially advanced or the flow of coolant is shut off or reduced in order to increase the combustion-chamber surface temperature. The point in time at which the general combustion takes place is considered to be the point in time when a fuel conversion rate of 50% of the charge has been reached.
In another embodiment of the invention, in the heating mode, the combustion is temporarily delayed with respect to standard operation, while predetermined limits for a combustion-chamber surface temperature are maintained.
Delaying the combustion results in a high exhaust-gas temperature and a poor thermodynamic efficiency of the internal combustion engine. It is ensured that predetermined limits for a combustion-chamber surface temperature are maintained, in order to avoid misfiring and to allow the internal combustion engine still to run smoothly. The high exhaust-gas temperature and the poor thermodynamic efficiency result in a high heat output and a maximum generation of heat in the internal combustion engine. As a result, the coolant can be heated rapidly in order to achieve a satisfactory heating comfort. In addition to a particular cold-start mode, these measures can also be carried out in partial-load mode in order to prevent the engine from cooling down. Such a cooling of the engine may result from the fact that cooling systems are generally designed for maximum demands, for example when driving uphill with a trailer in full-load operation at high ambient temperatures.
In still another embodiment of the invention the idling speed is increased in the heating mode as compared to standard operation, while the oil temperature and the coolant temperature are monitored.
This measure also contributes to the coolant temperature being increased to a level which ensures a satisfactory heating comfort.
In a further embodiment of the invention, in the heating mode, the flow of coolant through the internal combustion engine is blocked for a predetermined period of time after a cold start.
In this way, a combustion-chamber surface temperature can be rapidly increased to a level which allows the internal combustion engine to be operated with poor thermal efficiency as quickly as possible after a cold start. A blockage of the flow of coolant through the internal combustion engine is achieved, for example, by shutting down an electric cooling-water pump or by diverting the flow.
In a refinement of the invention, in heating mode, the flow of coolant through the internal combustion engine is controlled as a function of the combustion-chamber surface temperature and of the engine operating point.
In this way, it is possible to maintain a combustion-chamber surface temperature within a predetermined range.
In a further refinement of the invention, in the heating mode, an exhaust-gas re-circulation rate in an exhaust-gas re-circulation device of the internal combustion engine is set to a maximum possible value within predetermined limit values.
The limit values for the exhaust-gas re-circulation rate are determined by the smooth running of the engine, emission of pollutants and fuel consumption. A high exhaust-gas re-circulation rate results in a high thermal output from an exhaust-gas re-circulation heat exchanger. A high exhaust-gas re-circulation reduces the mass flow of cold fresh air, and leads to reduced heat losses on account of the reduced mass flow of exhaust gas being discharged. An exhaust-gas re-circulation rate is advantageously increased to such an extent that a cloudiness value of the exhaust gas remains just below the visibility limit.
In a further refinement of the invention, in order to increase the exhaust-gas re-circulation rate in the heating mode, the charging pressure of a supercharging device of the internal combustion engine is increased.
In this way, the amount of heat which can be removed from the engine and an exhaust-gas re-circulation cooler can further be increased. In addition, the dynamic properties of the vehicle can be improved, since the exhaust-gas temperatures are significantly higher than during standard operation, so that the charge pressure can be built up with less delay because of greater turbine output.
In a further refinement of the invention, in the heating mode the air flow through a charge-air cooler of a supercharging device of the internal combustion engine is set to zero (bypass).
This measure also contributes to the internal combustion engine or the coolant in the internal combustion engine being heated as quickly as possible.
Furthermore, in the heating mode, a radiator shutter is closed.
In still another refinement of the invention, in order to shift the combustion timing in the heating mode with respect to standard operation, a change is made to the injection quantities and/or injection times of a pre-injection, main injection and/or after-injection. Furthermore, in the heating mode, the injection pressure can be increased in order to increase the fuel injection quantity.
With a view to increasing the pressure and enlarging the injection quantity, it is for example possible to carry out a double, triple or multiple pre-injection, the individual injections being carried out at variable intervals both with respect to one another and with respect to the main injection quantity. This ultimately results in the center of combustion being shifted to an earlier time and possibly an increase in the combustion-chamber pressure up to the maximum permissible level.
In still a further refinement of the invention, there is a control means for controlling the coolant temperature of the internal combustion engine, the combustion-chamber surface temperature and/or the engine oil temperature.
The coolant temperature may be recorded, for example, at the coolant outlet of the internal combustion engine for control purposes. By monitoring and controlling the coolant temperature, the combustion-chamber surface temperature and/or the oil temperature, it is possible to achieve heating which is as fast as possible without any risk of overheating damage.
In a control means, the coolant temperature at the coolant outlet of the internal combustion engine, the combustion-chamber surface temperature and the oil temperature are prioritized in that order.
In this way, the coolant temperature has the highest priority, so that comfort-oriented control is achieved. The control means has at least one controller with a variable control characteristic.
It is, for example, possible to use a controller with what is known as an automated state unit, in which a control range is divided into a plurality of sub-ranges, each with different control characteristics, as a function of the control deviation and the interfering variables. It is also possible to use a PI controller, which, above a predetermined threshold value, operates as a P-controller.
The problem with which the invention is concerned is also solved by a motor vehicle having an internal combustion engine and heating installation for carrying out the method according to the invention, in which there are means for monitoring variables which are characteristic of a heating state of the internal combustion engine operating state and means for optionally setting a heating mode for the internal combustion engine. In the heating mode, operating parameters of the internal combustion engine, while satisfying required output values, are set for a maximum possible introduction of heat into the coolant and/or the exhaust gas. Advantageously, there is a controllable coolant pump for controlling the flow of coolant independently of the engine speed. It is also advantageous if an exhaust-gas recirculation heat exchanger is provided in the coolant circuit.
These measures enable operation of the internal combustion engine to be optimized with a view to an intelligent heating comfort management. On the one hand, operation for the quickest possible heating of the coolant is possible, and on the other hand so is an operation with the minimum possible consumption and emission of pollutants. A separate, controllable heating water pump is advantageous.
In a particular embodiment of the invention, the exhaust-gas recirculation heat exchanger and a heater are connected in series in the coolant circuit. An arrangement of this type is particularly effective, since in the exhaust-gas recirculation heat exchanger the coolant is additionally heated and, immediately thereafter, is cooled again in the heater. In this way, the coolant can only cool down to an insignificant extent between the exhaust-gas re-circulation heat exchanger and the heater. As a result, with the abovementioned arrangement, the coolant reaches the highest possible temperature when it enters the heater.
Preferably, a bypass line for bypassing the coolant radiator and a mixing valve, which can be controlled by means of a central control unit, for setting the flow of coolant through the bypass line and the coolant radiator are provided.
As a result, means for effectively controlling the flow of coolant as a function of engine operating parameters are provided. It is advantageously possible to provide a cylinder head and/or engine block through which the coolant flows transversely and an engine enclosure which can be tightly sealed.
The invention will become more readily apparent from the following description of preferred embodiments thereof in conjunction with the drawings: